Kitten Package - Pismo Beach Veterinary Clinic



Ettinger & Feldman — Textbook of Veterinary Internal Medicine

Client Information Sheet

Mammary Gland (Breast) Tumors in Dogs and Cats        

Ruthanne Chun

 

|What are mammary gland tumors? |

|Mammary gland tumors are common in dogs and cats that are not spayed or in animals that were spayed. In dogs early spaying provides a strong protective |

|effect; dogs spayed before their third heat cycle are much less likely to develop a mammary gland tumor than dogs spayed after their third heat cycle. |

|Although the protective effect is not as large in cats, it is clear that early spaying is also of benefit to this species. Treatment with megestrol acetate |

|is also linked to the development of mammary tumors in animals. |

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|Mammary tumors are similar to breast tumors in people. Usually no symptoms occur other than finding a “lump” when petting your dog or cat. Uncommonly, |

|mammary tumors can bleed or become infected. Because some of these tumors are malignant, the can spread to other parts of the body and cause illness (loss of|

|appetite, weight loss, lethargy, etc.). |

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|What are the symptoms of mammary gland tumors? |

|Mammary tumors are similar to breast tumors in people. Usually no symptoms occur other than finding a “lump” when petting your dog or cat. Uncommonly, |

|mammary tumors can bleed or become infected. Because some of these tumors are malignant, the can spread to other parts of the body and cause illness, loss of|

|appetite, weight loss, or lethargy. |

|  |

|What tests are needed? |

|The diagnosis of a mammary gland tumor relies primarily on evaluation of a biopsy. A safe rule of thumb regarding mammary gland tumors is that about 50% of |

|these tumors are benign and 50% are malignant. Further, 50% of the malignant tumors in dogs can be cured with just surgery. Unfortunately, mammary gland |

|tumors in cats are almost always malignant. In dogs and cats, the smaller the tumor is at the time of diagnosis the better the outcome. |

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|Tests that may help your veterinarian define your pet's prognosis by checking for metastasis (spread of cancer) include the following: |

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|X-rays of the thorax and abdomen |

|Abdominal ultrasound |

|Biopsy of lymph nodes that drain the site of the tumor |

|Fine needle aspirate of lymph nodes that drain the site of the tumor |

|Blood work to evaluate overall health of pet |

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|What treatment is needed? |

|All dogs with benign mammary tumors can be cured with surgery. As mentioned above, 50% of dogs with malignant mammary gland tumors can be cured with surgical|

|removal of the mass. However, even if the tumor is completely removed with surgery, your dog may develop another mammary tumor in the future. For the 50% of |

|dogs with malignant tumors that cannot be cured with surgery, chemotherapy may also be offered (see discussion below). |

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|Factors that help your veterinarian decide whether your dog should be treated with chemotherapy rather than surgery alone include the following: |

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|The size of the tumor at the time of diagnosis |

|Whether or not the tumor site is ulcerated |

|If evidence exists of spread of the tumor to the lymph nodes, lungs, or other sites of the body |

|Characteristics of the tumor on microscopic examination |

|  |

|Some drugs that are commonly used to treat dogs with malignant mammary gland tumors are piroxicam, doxurubicin, and cyclophosphamide. Piroxicam is an |

|anti-inflammatory drug that also has anticancer activities. The main side effects of piroxicam include loss of appetite and vomiting secondary to stomach |

|irritation. The side effects may be minimized by giving the medication with food. If your pet has a diminished appetite, vomiting, or a change in the |

|consistency of stool while on piroxicam, discontinue the medication and contact your veterinarian. The other drugs listed are more traditional anticancer |

|drugs (i.e., chemotherapy drugs). |

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|Two equally important goals should be kept in mind when choosing chemotherapy to treat your pet: |

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|Control the tumor for as long as possible |

|Maintain a good to excellent quality of life throughout the duration of treatment |

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|The chemotherapy drugs used for dogs and cats are the same drugs used in people. Because maintaining a normal quality of life is a main goal, chemotherapy is|

|used somewhat less aggressively than in human medicine. Also, dogs and cats seem to be more tolerant of chemotherapy than people. They do not usually have |

|side effects as severe as those in people. However, because chemotherapy drugs affect rapidly dividing cells, side effects can occur in dogs and cats. |

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|Two important sets of cells in the body naturally grow and divide rapidly. These are the following: |

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|The cells that line the bone marrow |

|The cells that line the gastrointestinal tract |

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|A complete blood count (CBC) should be performed immediately before and 7 to 10 days after your pet has chemotherapy. If the white blood cell count is low, |

|chemotherapy will be delayed 4 to 7 days; the counts will come back up on their own. Rarely the white blood cell count may drop so low that your pet is at |

|risk of developing an infection. In this situation, antibiotic therapy is indicated. At home, you may notice that your pet has a decreased appetite for 2 to |

|3 days after chemotherapy. You may also notice that they have softer stool than 4 to 7 days after chemotherapy. If you feel that vomiting or diarrhea is |

|severe, contact your veterinarian. Medication may be used to help minimize or control these side effects. |

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